Apparatus for controlling fuel injection timing in a fuel injection pump

ABSTRACT

In an control apparatus for controlling a timing of injection of fuel to be injected into an internal combustion engine, the apparatus comprises a closed loop system in which the data showing the actual timing of injection of of fuel is fed back. When the condition of the operation of the engine becomes a predetermined state, the control system is changed from the closed loop system to another system in which an adjusting member for adjusting the timing of injection of fuel is controlled by a signal which is not related to the actual timing of injection. As a result, the stability of the operation in low engine speed zone is remarkably improved.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for controlling theinjection timing of the fuel to be injected into an internal combustionengine.

For the purpose of electronically controlling the timing of the fuelsupply to an internal combustion engine in response to the operatingconditions of the engine, various types of apparatuses for controllingthe timing of fuel injection have been proposed (c.f. SAE 800167). Ingeneral, this type of apparatus has a sensor for detecting the timing ofa predetermined reference angle position (e.g. top dead center timing)of the crankshaft of the engine and another sensor for detecting theactual timing of fuel injection by a fuel injection pump and it is soarranged that the position of an injection timing adjusting member ofthe fuel injection pump is controlled in such a way that the actualtiming of injection as determined from the outputs from theabove-mentioned sensors is coincident with the optimum injection timingat each instant computed on the basis of operation parameters, such asthe rotational speed of the engine. The use of a closed loop system asmentioned above can be expected to realize highly accurate control ofthe timing of fuel injection. However, in the low rotational speed zoneof the engine, it brings about a disadvantage which impairs the stablecontrol condition. The reasons for this will be explained below.

In the low rotational speed zone where the amount of injection is rathersmall, the control conditions become unstable because the signalwaveform required for determining the actual injection timing cannot beobtained owing to the low level of the output signal from the sensor fordetecting the actual fuel injection timing (for example, a needle valvelift sensor provided in the fuel injection valve). Moreover, excessiveamplification of the sensor signal would decrease S/N ratio of thesignal and lead to erroneous operation. Further, a large error occurs inthe computation of the actual fuel injection timing because of the greatchanges that occur in the rotational speed within each combustion cycle.

Another disadvantage is that, in driving the injection timing adjustingmember by the use of a hydraulic timer or the like, since the oilpressure at low rotational speed is not sufficiently high for thecontrol of the adjusting member, the desired effect cannot be attainedeven if the closed loop system is employed.

SUMMARY OF THE INVENTION

An object of the present invention is, therefore, to provide an improvedapparatus for controlling the timing of fuel injection.

Another object of the present invention is to provide an electronicallycontrolled type apparatus for controlling the timing of fuel injection,which can accurately control the timing of fuel injection even in thelow rotational speed zone of the engine.

A further object of the present invention is to provide anelectronically controlled type of apparatus for controlling the timingof injection of fuel, in which the timing of injection of fuel iscontrolled by the use of a closed loop system during ordinary condition,and by the use of an open loop system when the engine speed is in apredetermined low rotational speed zone.

The apparatus for controlling the timing of injection of fuel accordingto the present invention has means for determining a target timing ofinjection in accordance with the operating conditions of the internalcombustion engine, means for detecting the actual timing of injection,means for detecting the difference between the target timing of theinjection of fuel and the actual timing of the injection of fuel, and anactuator for operating the injection timing adjusting member of the fuelinjection pump. When the internal combustion engine is in apredetermined normal operation mode, for example when it is operated ata speed higher than the predetermined rotational speed, a closed loopcontrol is carried out in such a way that the actuator is driven inaccordance with the above difference and the actual timing of injectionis made coincident with the target timing of injection. On the otherhand, when the internal combustion engine is operated in a mode otherthan the normal operating mode mentioned above, the timing of injectionis controlled by employing an open loop in which the actuator is drivenby a driving signal produced from another signal generator.

As for the predetermined operating conditions for switching between theclosed loop system and the open loop system herein, any appropriatecondition indicating the fact that the rotational speed of the enginehas become lower than the predetermined value, can be selected. Forexample, it is possible to select the condition that the adjustingmember for adjusting the amount of fuel injected is located beyond apredetermined position in the direction of decreasing amount of fuelinjection, or that the operating amount of an accelerator has becomeless than a predetermined amount. Whe the control mode is changed uponsensing these conditions which indicate that the engine is operating inthe low rotational speed zone, the timing of the injection of fuel iscontrolled by the use of an open loop system which may provide aconstant timing of the injection of fuel, or in case of a hydraulictimer etc., may control the timing in accordance with the rotationalspeed of the engine, that is, the oil pressure. Therefore, dataindicating the actual timing of the injection of fuel is not requiredand the fuel injection control can be carried out in a stable conditionsince the unstable factors due to the low engine speed are not fed back.On the other hand, when the engine is operating in other than the lowrotational speed zone, highly accurate control on the injection timingcan be carried out by the use of the closed loop system.

The invention will be better understood and the other objects andadvantages thereof will be more apparent from the ensuing detaileddescription of a preferred embodiment taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of the controlapparatus for controlling the timing of injection of fuel of the presentinvention;

FIGS. 2A and 2B are waveforms of the first and second pulse trainsignals, respectively;

FIG. 3 is a flow chart of the control program to be stored in amicrocomputer when a circuit block enclosed by the broken line in FIG. 1employs a microcomputer; and

FIG. 4 is a block diagram illustrating another embodiment of the controlapparatus for controlling the timing of injection of fuel of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a block diagram of an embodiment of an apparatus forcontrolling the timing of injection of fuel according to the presentinvention. The control apparatus 1 is an apparatus for controlling thetiming of injection of fuel by a fuel injection pump for injecting fuelinto an internal combustion engine, and in this embodiment, it is anapparatus for electronically controlling a hydraulic timer 4 provided ina distribution type fuel injection pump 3 so as to control the timing ofinjection of fuel of the fuel injection pump 3 for distributing andsupplying fuel to each cylinder of a four-cycle four-cylinder Dieselengine 2. The control apparatus 1 has a first detector 5 including aneedle valve lift sensor (not shown) which is mounted on one of the fuelinjection valves (not shown) mounted on a cylinder of the Diesel engine2, and a second detector 6 including a top dead center (T.D.C.) sensor(not shown) which is adapted to produce a pulse for every 1/2 rotationof the crankshaft of the engine. The first detector 5 generates a firstpulse train signal S₁ which consists of pulse signals P₁₁, P₁₂, P₁₃, . .. produced one each time the needle valve of the fuel injection valve islifted, and, the second detector 6 generates a second pulse train signalS₂ which consists of pulse signals P₂₁, P₂₂, P₂₃, . . . , which areproduced one each time any one of the predetermined pistons of theengine reaches its top dead center (See FIG. 2B).

In this embodiment, since the Diesel engine 2 is a four-cylinder,four-cycle engine, one pulse is generated from the first detector 5every time four pulses are generated from the second detector 6, asshown in FIGS. 2A and 2B. The pulse train signals S₁ and S₂ are appliedto a first computing circuit 7 where the difference in timing betweeneach pulse P₁₁, P₁₂, . . . of the first pulse train signal S₁ and eachcorresponding pulse P₂₁, P₂₅, . . . of the second pulse train signal S₂is computed as the difference in rotational angle of the crankshaft, andthe result of this computation is output as first data D₁ indicative ofthe actual timing of the injection of fuel at each instant.

On the other hand, a second computing circuit 8 is provided forcomputing the optimum timing of injection of fuel in accordance with theoperating conditions of the Diesel engine 2 at each instant. Speed dataD_(N) indicative of the rotational speed of the Diesel engine 2,acceleration data D_(A) indicative of the amount of operation of theaccelerator pedal (not shown), sleeve position data D_(R) indicative ofthe position of a control sleeve and coolant temperature data D_(T)indicating the temperature of the engine coolant are applied to a secondcomputing circuit 8 from a sensor unit 9 and the optimum timing ofinjection of fuel according to the operating condition of the engine ateach instant is computed in response to these input data. The computedresult is output as second data D₂ indicating the target timing ofinjection of fuel. The second computing circuit 8 can be arranged, forexample, in such a way that various data on injection timing are storedin a ROM in advance and, by applying address values determined by eachinput data, to the ROM as address signals, the data indicating therequired target timing of the injection of fuel can be read out from theROM in accordance with the combination of the input data.

The first and the second data D₁ and D₂ produced from the first andsecond computing circuits 7 and 8 are output as binary digital data andthese data are added in an adder 10 with the polarities shown in thefigure, producing error data D₃ indicating the difference between thedata D₁ and D₂. The error data D₃ is applied to a PI control circuit 11to be subjected to data processing required for proportional andintegral control and the resulting output is produced as data D₄ forclosed loop control. The data D₄ for closed loop control is applied to apulse width modulator 13 through a switch 12 and a driving pulse signalS₃ whose duty cycle changes in accordance with the data D₄ is producedfrom the pulse width modulator 13. The signal S₃ is applied, as anON/OFF control signal, to a solenoid valve 14 for timing control of thehydraulic timer 4.

The fuel pressurized in the fuel injection pump 3 is supplied to thetimer 4 through an opening 16 of a casing 15 of the timer 4, and thepressurized fuel passes into a chamber 19 through an orifice 18 definedin a timer piston 17 in the casing 15. As a result, the timer piston 17is pressed in the lefthand direction of FIG. 1. The timer piston 17 isbiased in the righthand direction of FIG. 1 by an expansion spring 20 soas to be positioned where the force of the expansion spring 20 iscoincident with the fuel pressure in the chamber 19. The chamber 19 isconnected with a fuel tank (not shown) through a pipe 21 having thesolenoid valve 14. Since the average opening area of the solenoid valve14 changes in accordance with the duty cycle of the driving pulse signalS₃, the fuel pressure in the chamber 19 will be determined by the dutycycle of the driving pulse signal S₃. Therefore, the timer piston 17 ispositioned in accordance with the data D₄ for closed loop control. Aroller holder 22 which is used for adjusting the timing of the injectionin the distribution type fuel injection pump 3, is connected with thetimer piston 17, and the rotational position of the roller holder 22 isadjusted in accordance with the position of the timer piston 17. As aresult, the control of the timing of injection of fuel by the timer 4 isperformed by using the closed loop system in accordance with the resultof a comparison of the actual timing of injection with the target timingof injection, and the actual timing of injection is controlled so as tobe coincident with the target timing of injection.

For the purpose of changing the control system of the timer 4 from theclosed loop system to the open loop system when the rotational speed ofthe engine becomes less than a predetermined low rotational speed, thecontrol apparatus 1 has a third computing circuit 23 for computing atarget timing of injection of fuel for open loop control which is usedwhen the engine speed is less than the predetermined engine speed, and aswitch control circuit 24 for discriminating whether or not the enginespeed is less than the predetermined engine speed.

As in the case of the second computing circuit 8, the speed data D_(N),the acceleration data D_(A), the sleeve position data D_(R) and thecoolant temperature data D_(T) are applied to the third computingcircuit 23 to compute the optimum timing of injection of fuel inresponse to these input data, and an open loop control data D₅indicative of the required duty cycle of the driving pulse signal S₃ forobtaining the optimum timing of injection of fuel, is producedtherefrom. The data D₅ is applied to the switch 12 and is supplied tothe pulse width modulator 13 in place of the data D₄ when the switch 12is changed over as shown by the broken line. As a result, the controlapparatus 1 is changed from the closed loop system to the open loopsystem.

The third computing circuit 23 can be arranged, for example, in such away that various open loop control data are stored in a ROM in advanceand the data stored in the ROM indicating the desired duty cycle isselected and read out from the ROM as the desired open loop control datain accordance with the combination of the input data when address valuesdetermined by the respective input data are applied to the ROM asaddress signals.

The speed data D_(N) is applied to the switch control circuit 24 and,when the rotational speed of the engine falls below the predeterminedvalue, the level of the output line 25 is changed from "L" to "H" andthe switch 12 is changed from the switching state shown by the solidline to that shown by the broken line. As a result, the open loopcontrol data D₅ is applied to the pulse width modulator 13 in place ofthe closed loop control data D₄ for closed loop control. Consequently,in the predetermined low rotational speed zone of the engine, the dutycycle of the driving pulse signal S₃ is controlled in accordance withthe open loop control data D₅ and the timer 4 is controlled inaccordance with the data D₅.

The circuit block 26 enclosed by the broken line can be constituted by amicrocomputer. FIG. 3 shows a flow chart of the program to be executedin the microcomputer in this case.

At first, in step 31, it is discriminated whether or not the enginespeed N is larger than the predetermined speed N₀, and when N>N₀, theactual timing of injection θ_(i) and the target timing of injectionθ_(s) are computed in steps 32 and 33, respectively, and the computationfor obtaining the error α between the target timing of injection θ_(s)and the actual timing of injection θ_(i) is carried out in accordancewith the formula θ_(s) -θ_(i) (step 34). The data D₃ indicating theerror α is subjected to the data processing required for PI control instep 35, whereafter the resulting output is converted into duty cycledata (data D₄ for closed loop control) which determined the duty cycleof the driving pulse signal S₃ to be applied to the solenoid valve 14.Then, the data D₄ is output in step 36 and is applied to the pulse widthmodulator 13 shown in FIG. 1, whereby the driving pulse signal S₃ whoseduty cycle changes in response to data D₄ is generated from the pulsewidth modulator 13.

When it is discriminated in step 31 that N≦N₀, the target duty cycle atlow speed is computed in step 37 and open loop control data D₅ isgenerated in step 37 to be applied to the pulse width modulator 13.

According to the above arrangement, when the rotational speed of theDiesel engine 2 is higher than the predetermined speed, since the timingof injection is controlled by means of the closed loop system in whichthe data D₁ indicating the actual timing of injection computed on thebasis of the timing pulses obtained from the first and second detectors5 and 6 is fed back, high accuracy control of the timing of injection offuel can be realized. On the other hand, when the rotational speed ofthe engine is lower than the predetermined value, the timer 4 iscontrolled by means of open loop control on the basis of the data D₅computed in the third computing circuit 23. Therefore, even if theamount of injection decreases, the amount of lift of the needle valve ofthe fuel injection valve decreases, a first pulse train signal S₁ ofsufficient level cannot be obtained, and the S/N ratio of the signaldrops to such extent that accurate computation for the actual timing ofinjection is difficult, control with high reliability can neverthelessbe executed free from any effect on the controlling operation forinjection timing. When the rotational speed of the engine falls, therotational speed in the combustion cycle changes, which makes accuratecomputation of the actual timing of injection difficult, and the controlbecomes unstable in case the closed loop controlling operation asdescribed above is employed. However, in the low rotational speed zone,the open loop control is started by the switching of the switch 12, andany adverse effect that might be caused by rotational speed changes inthe combustion cycle can be eliminated. That is, when the engine speedis low, since the timing of injection of fuel is controlled by the useof the open loop system, the control system of the timer 4 is notdisturbed by any disturbances due to various unstable componentsoccuring in low rotational speed condition and control with higherstability can be secured.

Though the above embodiment refers only to the control of timing ofinjection in a distribution type fuel injection pump, the presentinvention is not limited to this embodiment but is applicable toinjection timing control of other types of fuel injection pumps as well,such as the in-line type fuel injection pump and the like.

Also, though the above-mentioned embodiment is arranged so as to changeover from the closed loop system to the open loop system by switchingthe switch 12 in response to the fact that the rotational speed of theengine decreases below the predetermined value, it can be arranged toswitch in response to other operation parameters such as the amount ofoperation of the accelerator pedal, positions of the control sleeve andthe like. In other words, it can be arranged to control the timing ofinjection of fuel by the use of the open loop system when the strengthof the needle valve lift signal from the fuel injection valve is notsufficient as in the case that the amount of operation of theaccelerator pedal becomes less than a predetermined amount, or that thecontrol sleeve has gone beyond a predetermined position in the directionof decreasing the amount of fuel to be injected.

In the embodiment shown in the figure, since the pressure of fuelsupplied to the timer 4 changes in accordance with the rotational speedof the engine, the timer 4 tends to be not sufficiently driven in thelow rotational speed zone of the engine. Therefore, the apparatus may bearranged in such a way that the timing of injection is controlled inresponse to the rotational speed of the engine (fuel pressure suppliedto the timer 4) by maintaining the solenoid valve 14 in open or closedstate, or by applying pulse voltage having a predetermined constant dutycycle to the solenoid valve 14 while the engine is operating in the lowrotational speed zone, whereby stability of the operation in the lowrotational speed zone is more improved.

FIG. 4 shows another embodiment of a control apparatus 30 of the presentinvention, by which the purpose described above can be attained. In FIG.4, the same portions as those shown in FIG. 1 are designated by the samereference numerals. The control apparatus 30 is so arranged that thedata D₄ is directly applied to the pulse width modulator 13 and thedriving pulse signal S₃ is applied to the solenoid valve 14 through aswitch 27 which is controlled by the switch control circuit 24. Thecontrol apparatus 30 has a signal generator 26 instead of the thirdcomputing circuit 23, and a control signal S₄ produced from the signalgenerator 26 is applied to the switch 27. The swithc 27 is switched overas shown by the solid line to select the driving pulse signal S₃ whenthe engine speed is equal to or higher than a predetermined speed, andswitched over as shown by the broken line to select the control signalS₄ when the engine speed is less than the predetermined speed.

In this embodiment, the control signal S₄ is produced from the signalgenerator as a signal for maintaining the solenoid valve 14 open.

Therefore, when the engine speed becomes less than the predeterminedspeed, the closed loop system is switched out and the control is carriedout by the fuel pressure in the fuel injection pump 3.

The control signal S₄ may be a signal for maintaining the solenoid valve14 closed or a pulse signal having a constant duty cycle.

What is claimed is:
 1. An apparatus for controlling the timing ofinjection of fuel supplied to an internal combustion engine from a fuelinjection pump having a member for adjusting the timing of injection offuel, said apparatus comprising:means for operating said member; a firstmeans for generating a first signal relating to the actual timing ofinjection of fuel supplied from said fuel injection pump; a second meansfor generating a second signal relating to the target timing ofinjection of fuel determined by the condition of operation of saidinternal combustion engine; means responsive to said first and secondsignals for generating an actuating signal for driving said operatingmeans so as to make said actual timing of injection coincident with saidtarget timing of injection by closed loop control; a third means forproducing a third signal for driving said operating means, said thirdsignal being representative of a normal operating condition of theengine but unrelated to said actual timing of injection; means fordetecting whether or not said internal combustion engine is beingoperated in a predetermined low engine speed range; and means responsiveto the detected result of said detecting means for selectively applyingsaid actuating signal or said third signal to said operating means so asto select said third signal when the engine speed is within saidpredetermined low engine speed range and said actuating signal when theengine is not within said predetermined low engine speed range.
 2. Anapparatus for controlling the timing of injection of fuel supplied to aninternal combustion engine from a fuel injection pump having a memberfor adjusting the timing of injection of fuel, said apparatuscomprising:means for operating said member; a first means for generatinga first signal relating to the actual timing of injection of fuelsupplied from said fuel injection pump; a second means for generating asecond signal relating to the target timing of injection of fueldetermined by the condition of operation of said internal combustionengine; means responsive to said first and second signals for generatingan actuating signal for driving said operating means so as to make saidactual timing of injection coincident with said target timing ofinjection by closed loop control; a third means for producing a thirdsignal for driving said operating means, said third signal being aconstant value unrelated to said actual timing of injection; means fordetecting whether or not said internal combustion engine is beingoperated in a predetermined low engine speed range; and means responsiveto the detected result of said detecting means for selectively applyingsaid actuating signal or said third signal to said operating means so asto select said third signal when the engine speed is within saidpredetermined low engine speed range and said actuating signal when theengine is not within said predetermined low engine speed range.
 3. Anapparatus as claimed in claim 1 wherein said third means produces saidthird signal in response to at least one operating parameter showing thecondition of operation of said internal combustion engine to control thetiming of injection by an open loop system.
 4. An apparatus as claimedin claim 1 wherein said second means has a sensor unit for producing atleast one signal indicating the condition of operation of said internalcombustion engine, and a computing circuit which computes said targettiming of injection in response to at least one signal from a sensorunit and produces said first signal.
 5. An apparatus as claimed in claim1 wherein said first means has a first detector for detecting the timingat which the pistons of said internal combustion engine reach apredetermined reference position, a second detector for detecting thetiming of the beginning of injection of fuel from said fuel injectionpump into a cylinder of said internal combustion engine and a computingcircuit which computes the injection advance in response to the detectedresult of first and second detectors and produces a signal indicative ofthe computed result as said first signal.
 6. An apparatus as claimed inclaim 1 wherein said operating means is a hydraulic timer responsive tothe fuel pressure supplied from said fuel injection pump having a timerpiston which is connected with said member and a solenoid valve forregulating the fuel pressure applied to the timer piston.
 7. Anapparatus as claimed in claim 6 wherein said actuating signal generatingmeans has a circuit responsive to said first and second signals forgenerating an error signal showing the difference between said actualtiming of injection and said target timing of injection and a pulsewidth modulator responsive to the error signal for producing as saidactuating signal a pulse signal whose duty cycle changes in accordancewith the error signal, whereby to control the average opening area ofthe solenoid valve in accordance with the error signal.
 8. An apparatusas claimed in claim 6 wherein said third signal is a signal formaintaining said solenoid valve to open.
 9. An apparatus as claimed inclaim 6 wherein said third signal is a signal for maintaining saidsolenoid valve to closed.
 10. An apparatus as claimed in claim 1 whereinsaid detecting means operates in response to a signal indicative of thespeed of said internal combustion engine.
 11. An apparatus as claimed inclaim 3 wherein said third means has a memory in which various open loopcontrol data are stored in advance and a selected open loop control datais read out from said memory by the application of at least one signalindicating an engine operating parameter to generate said third signal.12. An apparatus according to claim 1, wherein said third signal isrepresentative of the engine coolant temperature.